ATCvet code: QC08CA01

Amlodipine is a calcium ion influx inhibitor of the dihydropyridine group (slow channel blocker or calcium ion antagonist) and inhibits the transmembrane influx of calcium ions into cardiac and vascular smooth muscle.

The mechanism of the antihypertensive action of amlodipine is due to a direct relaxant effect on vascular smooth muscle, where it acts as a peripheral arteriolar vasodilator and reduces afterload.

Amlodipine has a higher affinity for L-type calcium channels and has some affinity for T-type calcium channels. Within the kidney, L-type calcium channels are found primarily in afferent (prerenal) arterioles. Although amlodipine has a greater affinity for the vascular L-type calcium channels, it can also act on those found in the cardiac muscle and cardiac nodal tissue.

Amlodipine slightly depresses impulse formation and conduction velocity in the cardiac muscle.

In cats with systemic arterial hypertension, once daily dosing of amlodipine by oral route provides clinically significant reductions of blood pressure throughout the 24 hour interval. Due to the slow onset of action, acute hypotension is not a feature of amlodipine administration.

Absorption: After oral administration amlodipine is well absorbed with a mean bioavailability of approximately 80%. Following a single dose of 1 mg per cat (corresponding to 0.16 and 0.40 mg amlodipine/kg) peak blood levels of 3.0-35.1 ng/ml (mean Cmax 19.3 ng/ml) are measured between 2-6 hours (mean Tmax 4.3 hours) post dose.

Distribution: Amlodipine is highly bound to plasma proteins. In vitro protein binding in cat plasma is 97%. The amlodipine volume of distribution is approximately 10 L/kg.

Biotransformation: Amlodipine is extensively metabolized in the liver to inactive metabolites.

Elimination: Amlodipine has a long plasma half-life of 33-86 hours (average 54 hours), resulting in significant accumulation.